Manufacture of nitrates



May 13, 19"-1-1` H, PAULING 2,241,613

MANUFAGTURE oF NIfTRATEs Filed March 10, 1938 Hafrrrlg Paul/ng PatentedMay 13, 1941 2,2%!613 MANUFACTURE OF NITRATES Harry Pauling, Berlin,Germany application March 10, 193s, :serial No. 195,152 InCzechoslovakia. March i27, 1937 Claims.

It is known to manufacture the nitrates of alkalies, alkaline earths andammonia by reacting the chlorides with nitric acid and removing theresulting hydrochloric acid from the reacting mixture by distillation.In order to prevent the decomposition of the nitric acid by thehydrochloric acid, that is to say, the formation of nitrosyl chlorideand chlorine, it has already been proposed to carry out the reaction invacuo, and for the distillation of the hydrochloric acid withsimultaneous evaporation of the water, to pass superheated steam intothe reaction mixture. This method of evaporating the salt liquorrequires very considerable quantities of steam, whereby not only is theresulting hydrochloric acid very considerably diluted, but also reactionapparatus of large dimensions is necessary.

In accordance with the invention, the difliculties of the knownprocesses are overcome by the fact that the conversion of the chloridesby means of nitric acid is not effected as heretofore at the lowestpossible temperature but at the highest possible temperature, andfurthermore steam at atmospheric pressure is introduced, in so far as itis not produced by evaporation of the nitrate liquor which is likewisecarried out at atmospheric pressure. 'Ihe present process employs inthis case nitric acid in excess, so that after completion of thereaction, chlorine ions are no longer present in the reaction mixtureand consequently the evaporation of the nitrate liquor containing nitricacid can take place in apparatus made of ordinary materials. As,furthermore,

according to the present process, strong nitric acid may be employed,the hydrochloric acid is obtained directly in the commercialconcentration of about 33%.

In accordance with theinvention, the reaction takes place in acounter-now. device comprising two stages, for example in a column whichis combined with an evaporator. To the upper stage water is supplied, ifdesired together with a part of the chlorides to be converted, and tothe lower stage are supplied aqueous nitric acid, mother liquorresulting from the separation of the nitrate, and the chloride, in sofar as the latter is not already supplied to the upper stage. From thelower stage of the counter-flow device, the reaction mixture passes forevaporation under atmospheric pressure into an evaporator, from which onthe one hand the vapour mixture generated is passed into the lower stageof the counter-flow device, and on the other hand the nitrate liquor ispassed into a crystalliser for the separation of the nitrate.

It is also possible, however, to pass the nitrate liquor first into thecrystalliser, because it is already very strongly satura-ted. Theprincipal part of the sodium nitrate is separated out in thecrystalliser. From the crystalliser the liquor passes into theevaporator, the vapours of which are led into the lower stage of thecounter-flow device, while the evaporated liquor is returned to thecrystalliser.

A further improvement in the method of Working is secured by providingbetween the lower part of the counterflow device, on the one hand, andthe evaporator on the other, a second, smaller additional counter-flowdevice, for example a column, through which are passed the vapourscoming from the evaporator and if desired steam supplied from outside,before these enter the lower part of the counter-How device. The liquorpasses from the lower part of the counter-flow device first through theadditional column and only then, according to the method of working,either into the crystalliser or into the evaporator. This additionalcounter-flow device makes it possible to employ a very considerableexcess of nitric acid, which excess however, does not enter thecrystalliser or evaporator because it is evaporated in the additionalcolumn and thus enters the counter-flow device. In this way the nitricacid content is kept low in accordance with the quantity of steam andthe conditions of equilibrium between the steam and the nitric acidVapour, so that crystallisation does not require to be repeated.

A ow diagram illustrating the processes disclosed herein is illustratedin the drawing.

The two part counter-flow device shown consists of an upper part a, anda lower part b. Each of these parts is in itself a counter-how deviceand is provided either with a charging device, bell bottoms or the likeinstallations. Water is supplied to the upper part a through a conduitc, if desired with a part of the chloride to be converted, and to thelower part b are supplied, through a conduit d, the aqueous nitric acid,the circulating mother liquor` and the residual part of the chloridewhich has not yet been supplied to the upper part a; in addition watermay also be supplied at this place. From the lower part b of thecounter-flow device, the liquor ows through a conduit e into anauxiliary small counter-now device j and thence through a conduit g`into an evaporator h and from the latter through a conduit i into acrystalliser k. The liquor may also be led through a conduit l firstinto the crystalliser 1c and thence through a conduit m into theevaporator h, and after evaporation returned again to the crystalliser.The mother liquor produced in the crystalliser is returned throughconduits s and d to the stage b of the counter-flow device and the saltis removed from the crystalliser through an outlet t.

From the evaporator h, the vapours pass through a conduit n into theauxiliary counternow device f, into which steam may also be introducedthrough a conduit o. From the auxiliary counter-flow device f, thevapours are passed through a conduit p into the stage b of the maincounter-now device.

The crystalliser may be made of the known silicon cast iron or of V2Asheet metal, because chlorine ions are no longer present in the liquor,while the evaporator is preferably made of silicon cast iron vessels,which nowadays can be supplied for the evaporation of liquids containingnitric acid, up to the largest dimensions required industrially.

The hydrochloric acid escapes from the counter-now device through aconduit q into a condenser r which is cooled to as low a temperature aspossible.

Since the heating of the liquids within the counter-now device causesdilution through condensing water, they may be heated indirectly, beforethey enter the counter-now device, at a suitable point outside thecounter-flow device by means of the vapours generated during theprocess. rIhis step, however, does not make any difference in the heatrequirement of the process, but merely results in the fact that a largerquantity or water may be supplied to the upper part of the device, whilefurther below the addition of water should be correspondingly reduced.

The process according to the invention is based on the following facts:In the lower part b of the counter-now device, the nitric acid mainlyreacts with the chloride to form nitrate and free hydrochloric acid, thehydrochloric acid being converted to a considerable extent into vapouron account of its volatility. In addition to this reaction, however, asecondary reaction takes place to a very considerable extent accordingto the following equation, namely the so-called aqua regia reaction:

This reaction becomes very prominent, both with increasing temperatureand also with the concentration of the reaction components, to such anextent in comparison with the nitrate formation that heretofore it hasdeterred all investigators from following up the reaction, which hasbeen regarded as unserviceable.

The inventor has, however, found that the aqua regia reaction is areversible reaction, and that if the reaction products are passedthrough a relatively weak mixture of the components taking part or evenonly through pure water, the nitrosyl chloride and the chlorine in thewater again form quantitatively nitric acid and hydrochloric acid, andthat surprisingly, this reaction proceeds all the more rapidly and allthe more completely, the higher the temperature, providaafiil ed onlythe concentration proportions are suitably selected and suicient time isallowed for the reaction proceeding in the reverse direction.

The process may also be carried out by employing chlorides of thealkalies, of ammonia and of the alkaline earths alone or in admixture.

Having now particularly described and ascertained the nature of my saidinvention and in what manner the same is to be performed, I declare thatwhat I claim is:

1. A method for the production of nitrates and hydrochloric acid fromchlorides capable of metathetical reaction with nitric acid whichcomprises treating such chlorides at boiling temperature and atatmospheric pressure in a countercurrent reaction zone with an excess ofstrong nitric acid to form a nitrate liquor and a gasvapor mixturecontaining substantial quantities of nitrosyl chloride and chlorine,reacting the gasvapor mixture containing substantial quantities ofnitrosyl chloride and chlorine eiiluent from said reaction zone atelevated temperatures under atmospheric pressure with water incountercurrent in a second treatment zone beyond that in which nitricacid is introduced to the process, whereby substantially all of thenitrosyl chloride and chlorine are converted into aqueous nitric acidwhich is returned to the reaction zone and gaseous hydrochloric acidwhich is ejected as such from said zone, and condensing the saidhydrochloric acid.

2. A process asset forth in claim 1 in which the nitrate liquor isheated in an evaporating zone and the vapor formed in the evaporatingzone is passed into the reaction zone countercurrent to the reactantstherein.

3. A process as set forth in claim 1 in which the nitrate liquorsubstantially free from hydrochloric acid is passed into a third zone incountercurrent to steam supplied to said third zone from an externalsource, and the steam and acid vapors formed in said third zone arepassed into the reaction zone in countercurrent to the reactantstherein.

4. A process as set forth in claim l in which the nitrate liquorsubstantially free from hydrochloric acid is passed into a third zone incountercurrent to steam supplied to said third zone from an externalsource, the steam and acid vapors formed in said third zone are passedrinto the reaction zone in countercurrent to the reactants therein,heating the nitrate liquor in an evaporating Zone, passing vapors formedin said evaporating Zone into the said third zone countercurrent to thefiow of liquor therein, subjecting the concentrated liquor formed in theevaporating zone to crystallization for the recovery of nitratestherefrom, and returning the mother liquor from said crystallization tothe reaction zone.

5. A process as set forth in claim 1 in which part of the chloride usedas a reactant is supplied with water to the Zone in which the nitrosylchloride rand chlorine are converted into aqueous nitricacid and gaseoushydrochloric acid, and the remainder of the chloride is supplied withaqueous nitric acid in the reaction zone.

HARRY PAULING.

